Railway Empire 2

Holding RT and selecting the icon with the top hat (top right), which is the Company screen, tab RB a couple of times to competitors and you're able to buy shares in your competitors (I done this on Campaign 1 once I completed all tasks and it allows you to continue, where you have just one competitor)

Once you've got 100% of the company it will start giving you their income, but this only popped for me once I pressed X, when highlighting the competitor, to do a Merger